1. Field of the Invention
The invention relates to a switching power amplifier for supplying an audio output signal.
2. Description of the Related Art
From the European patent application EP-A-0930700, a known class D amplifier receives at an input a PCM input signal. Using traditional class D technology any of three imperfections, that is efficiency, linearity or EMI, may be improved upon with the expense of at least one of the other two. The switching frequency is directly proportional to the required signal bandwidth. Further the high repetition rate of for example DSD (Direct Stream Digital) will translate into a vary high switching noise and thus low efficiency. A DSD signal is a representation of an audio signal using the following parameters. Sampling rate=64 or 48 times 44.1 kHz. One bit, noise shaped. Maximum modulation index=50%. Using bandwidth 60 kHz, spectral information up to 100 kHz.
It is an object of the invention to improve the known switching power amplifier.
To this end a switching power amplifier according to the invention comprises an input unit for receiving an input signal, a plurality of parallel low power switching power stages for outputting a plurality of output signals, a driving unit to drive the power stages in response to the input unit receiving the input signal, and a summation unit for summing the output signals of the power stages. The precision and efficiency of a switching power amplifier is improved by combining a plurality of low-power switching power stages into a larger amplifier. In this way it is made possible to increase the efficiency of the switching power amplifier without deteriorating the other imperfections.
The advantages of multiple phases are: output switches will need to supply only a fraction of the total power, the switches are smaller and hence switch faster, with less losses, the number of output transitions is distributed across these smaller switches, and the influence of a timing error on one switch will be 1/n of what it would have been with a single phase.
A specific drive method is used to allow for low-loss combination of the signal voltages. An inductive combiner is devised to provide error-free combination. This method allows for direct conversion of for example DSD signals into analog power with low distortion and high efficiency.